1. Field of the Invention
The present invention relates to a pixel structure and a method for manufacturing thereof and, more particularly, to a pixel structure having a shielding electrode and a method for manufacturing thereof.
2. Description of Related Art
The thin film transistor liquid crystal display (TFT-LCD) mainly includes a TFT array substrate, a color filter substrate, and a liquid crystal layer disposed between the TFT array substrate and the color filter substrate. The TFT including a gate, an active layer, a source, and a drain is usually adopted as a switch. The TFT includes an amorphous silicon (a-Si) TFT and a poly-silicon TFT according to the material of the active layer. The poly-silicon TFT has less power consumption and better electron mobility in comparison with the a-Si TFT. Moreover, an LCD using a low temperature poly-silicon TFT as a switch has advantages of slimness, compactness, high resolution, and so forth. Thus, the low temperature poly-silicon TFT is frequently deployed in portable products that demand low power consumption.
The pixel structure of the conventional poly-silicon TFT LCD includes a scan line, a data line, a poly-silicon TFT, and a pixel electrode. Here, the distance between the pixel electrode and the data line is a major factor determining the aperture ratio of the pixel structure. Said aperture ratio directly affects the backlight source utilization and further influences display brightness of the LCD. In the pixel structure, the parasitical capacitance Cpd (capacitance between the pixel electrode and the data line) increases as the distance between the pixel electrode and the data line is excessively decreased. Thereby, the potential of the pixel electrode is affected by the signal transmitting in the data line when the poly-silicon TFT is switched off, which leads to a cross-talk effect and further to deterioration of the display quality of the LCD.
To reduce the cross-talk effect induced in the pixel structure without affecting the aperture ratio of the pixel structure, many designs of pixel structures have been developed one after another.
FIG. 1 is a schematic cross-sectional view of a conventional pixel structure. Referring to FIG. 1, the conventional pixel structure 100 disposed on a substrate 110 includes a scan line (not shown), a data line 130, an active device 140, a pixel electrode 150, and a planarization layer 160. Both the scan line and the data line 130 are disposed on the substrate 110. The active device 140 is disposed on the substrate 110 at the intersecting place between the scan line and the data line 130 and is electrically connected to the scan line and the data line 130. The pixel electrode 150 is electrically connected to the active device 140. The planarization layer 160 is disposed over the substrate 110, such that an edge of the pixel electrode 150 extends over the data line 130 so as to increase the aperture ratio.
The thickness of the planarization layer 160 is greater than other layers and is often fabricated with a low dielectric constant (low-K) material. Hence, the influence of the parasitical capacitance Cpd on the pixel electrode 150 is reduced. However, the organic material e.g. acrylic resin widely-used in a manufacturing process of the planarization layer 160 is likely to deteriorate the adhesive strength due to its superior water absorptivity. In addition, the transmittance of the pixel structure declines since the material of the organic material cannot be completely bleached.
On the other hand, in the pixel structure 100, the storage capacitor is formed by a first metal layer 144 (an upper electrode) and a poly-silicon layer 142 (a bottom electrode), and the performance of the storage capacitor relates to the electrical conductivity of the upper and the bottom electrodes. Since a portion of the poly-silicon layer 142 is covered by the first metal layer 144 disposed over the poly-silicon layer 142, an ionic doping process of the poly-silicon layer 142 cannot be performed with ease, and therefore the electrical conductivity of the poly-silicon layer 142 is reduced. To enhance the performance of the storage capacitor to a certain degree, the driving potential is correspondingly increased.